Grouting compositions have been used for many years to minimize the movement of water and other fluids into, through, and out of wells and other subsurface cavities. Historically, these compositions were often comprised of neat cement, or cement-sand-gravel mixtures. These grout compositions had the disadvantage of being troublesome to place and often failed to fully fill the subsurface void. Even when up to about 5% bentonite was added to the cement mixture as a plasticizer and flow control agent complete filling of all subsurface voids remained a problem. Additionally, all of the cement mixtures tend to shrink upon curing, resulting in loss of seal integrity and increased fluid flow.
More recently various bentonite based grouting compositions have been developed which eliminate many of the problems associated with the cement based compositions. U.S. Pat. No. 2,861,636 (Messenger) describes a clay cement for use in correcting lost circulation problems in well bores which employs bentonite in combination with activated silica, activated alumina or activated silica-alumina and a water soluble phosphoric acid salt. U.S. Pat. No. 3,028,913 (Armentrout) describes a composition for use in recovering lost circulation in wells in which one embodiment consists of bentonite with a metallic chloride inhibitor and a porous inert material impregnated with a metallic hydroxide accelerator. U.S. Pat. No. 3,111,006 (Caron) describes a composition for use in soil solidification composed of clay, which may or may not include bentonite, an alkali silicate such as sodium silicate and at least one alkali phosphate salt.
U.S. Pat. No. 4,463,808 (Mason et al.) describes a composition in which bentonite, especially granular bentonite, is added to a premixed water and polymer solution which inhibits the swelling of the clay for a sufficient period of time to allow the fluid grout to be placed in a well borehole for the purpose of plugging the borehole. U.S. Pat. No. 4,886,550 (Alexander) describes a composition for cementing, sealing, plugging and grouting wells and boreholes consisting of a water swellable clay such as bentonite, an optional non-water swellable particulate filler which may be calcium bentonite, and an inorganic dispersing agent such as sodium acid pyrophosphate. U.S. Pat. No. 5,021,094 (Brown et al.) describes a composition for sealing a borehole or other subterranean cavity comprised of powdered swellable colloidal clay, such as bentonite, with a thinner, most especially a low molecular weight polyacrylate polymer, which acts to delay the onset of gelling thereby enabling higher concentrations of swelling clay to be used than would otherwise be possible.
The compositions described by Messenger, Armentrout, and Caron are complex combinations using expensive chemicals and requiring a great deal of effort and sophistication to prepare. As a result, they are too expensive to be used in general water well and mineral exploration borehole plugging and abandonment. The composition described by Mason, et al suffers from the fact that it has a strong tendency to hydrate prematurely, before it can be properly placed, and thereby frequently causes plugging of mixers, pumps and conveying hoses and pipes. The compositions described by Alexander and Brown, et al., require that significant concentrations of the compositions be used in the prepared grout, normally about 30% by total weight of the prepared grout, in order to yield a grout mixture which will properly gel or set up within a borehole. The high composition usage rate required by these inventions makes them prohibitively expensive for many types of plugging and abandonment work due to the large volumes of grout slurry typically required by these applications. The composition of the present invention improves on or solves each of the deficiencies described for the aforementioned prior art compositions.